Abstract

Works presented in this paper have been performed within the GARTEUR Action Group AG15 “Improvement of SPH methods for application to helicopter ditching” whose overall objective aimed at assessing analytical tools for the simulation of helicopter impacts on water. It especially focused on the Smooth Particle Hydrodynamic (SPH) formulation which consists of a gridless Lagrangian method and whose main interest, with respect to fluid/structure interaction issues, relies upon the absence of connectivity between the “particle elements”, thus permitting to cope with large deformations without generating mesh distortion problems.
In a first step, the SPH method was evaluated through the simulation of droplets impact tests onto rigid plate, performed at two impact velocities (1 m/s and 5 m/s); numerical results were analysed in terms of force and impulsion data and proved to conveniently fit with the tests results.
In a second step, water impact tests on simple shapes were simulated. On the one hand, tests on triangular and cylindrical rigid shapes, performed at Politecnico Di Milano, were considered; specimens were instrumented with pressure transducers and accelerometers and were tested at two velocities (4.4 m/s and 7.7 m/s). Numerical results proved to be in good agreement with the experimental data, with a convenient prediction of the acceleration peaks and pulse durations, and a satisfactory estimation of the order of magnitude of the pressure data. On the other hand, simulations of vertical drop tests on water of a deformable metallic cylinder were conducted. Tests were performed at CIRA, for 3 increasing velocities (3m/s, 8m/s and 10 m/s), with measurements including pressure data, acceleration data, high speed videos and residual deformation of the article. For the simulated structures and impact conditions, simulations permitted to draw general conclusion in terms of numerical prediction regarding deformations, accelerations and pressures data.